The invention pertains to methods for etching silicon dioxide, and in particular embodiments pertains to methods for altering the selectivity of an etch for silicon dioxide relative to silicon nitride. The invention also pertains to methods of forming isolation regions.
Silicon dioxide materials are commonly used in fabrication of semiconductor devices. Accordingly, numerous semiconductor fabrication processes involve etching of silicon dioxide materials. Another commonly used material in semiconductor fabrication processes is silicon nitride. In various processes, it can be desired to adjust etch selectivity for silicon dioxide relative to silicon nitride. For purposes of interpreting this disclosure and the claims that follow, the term xe2x80x9cetch selectivityxe2x80x9d refers to a rate of removal of one material relative to another material. For instance, an etch which is selective for silicon dioxide relative to silicon nitride is defined as an etch which removes silicon dioxide faster than silicon nitride. Adjustment of etch selectivity is defined to mean alteration of the rate of an etch of one material relative to another material. For instance, adjustment of etch selectivity for silicon dioxide relative to silicon nitride means that the rate of removal of silicon dioxide relative to silicon nitride is either increased or decreased.
An exemplary prior art process wherein it can be desired to adjust etch selectivity for silicon dioxide relative to silicon nitride is described with reference to FIGS. 1-4. Referring initially to FIG. 1, a semiconductor wafer fragment 10 is illustrated. Wafer fragment 10 comprises a substrate 12 which can comprise, for example, monocrystalline silicon lightly doped with a background of p-type dopant. To aid in interpretation of the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
A silicon dioxide layer 14 is formed over substrate 12, and a silicon nitride layer 16 is formed over silicon dioxide layer 14. Oxide 14 is provided to alleviate stresses that could occur if nitride 16 were placed directly on substrate 12. For purposes of interpreting this disclosure and the claims that follow, a layer referred to as a xe2x80x9csilicon dioxide layerxe2x80x9d is a layer which comprises silicon dioxide, but it not a layer which consists essentially of, or consists of, silicon dioxide unless such is stated explicitly. Also, a silicon nitride layer is a layer which comprises silicon nitride, but is not a layer which consists of, or consists essentially of, silicon nitride unless such is stated explicitly.
Silicon nitride layer 16 and silicon dioxide layer 14 are patterned and have an opening 18 extending therethrough. Silicon nitride layer 16 and silicon dioxide layer 14 can be patterned utilizing photoresist (not shown) and photolithographic processing.
Referring to FIG. 2, opening 18 is extended into substrate 12.
FIG. 3 shows an insulative material 20 formed within opening 18 a and over silicon nitride material 16. Insulative material 20 can comprise, for example, silicon dioxide.
Referring to FIG. 4, the silicon dioxide material 20 from FIG. 3 is subjected to an etch, such as, for example, chemical-mechanical polishing, to remove the silicon dioxide material 20 from over silicon nitride 16 while leaving material 20 within opening 18. The etch leaves an upper surface 22, which is intended to be a planarized upper surface. The material 20 remaining with opening 18 forms an isolation region, which can be utilized for electrically isolating conductive circuitry (not shown) formed over and/or within substrate 12.
A problem associated with the prior art processing is shown in FIG. 4 as a dishing of the top surface of material 20. Specifically, the chemical-mechanical polishing has removed silicon dioxide material 20 too rapidly relative to silicon nitride material 16, and has accordingly dished an upper surface of material 20, rather than forming a desired planarized upper surface. It would be desirable to develop methods wherein the selectivity of an etch for silicon dioxide relative to silicon nitride can be adjusted to alleviate or avoid the dishing shown in FIG. 4.
In one aspect, the invention encompasses a semiconductor processing method in which silicon dioxide is etched with a solution that comprises an alkyl peroxide. An exemplary alkyl peroxide is methyl peroxide.
In another aspect, the invention encompasses a method of forming an isolation region. A patterned silicon nitride material is formed over a semiconductive substrate. The patterned silicon nitride material has an opening extending therethrough. The opening is further extended into the substrate underlying the silicon nitride material, and is then filled with silicon dioxide. Subsequently, the silicon dioxide is chemical-mechanical polished with a slurry having an alkyl peroxide therein.